Pharmacokinetic and pharmacological profiles of free and liposomal recombinant human erythropoietin after intravenous and subcutaneous administrations in rats

Influence of route of administration and liposomal encapsulation on blood and lymph node exposure to the protein VEGF-C156S

VEGF-C156S is a recombinant form of human vascular endothelial growth factor C (VEGF-C), which targets the receptor VEGFR-3 present in the lymphatics. VEGF-C156S has lymphangiogenic properties and may represent a potential therapeutic approach in treating the lymphatic disease lymphedema. In the present study, we tested the hypotheses that (1) subcutaneous (s.c.) injection will provide higher lymphatic exposure than intravenous (i.v.) administration of VEGF-C156S and (2) s.c. injection of liposomal (s.c. Lipo) VEGF-C156S will provide greater lymphatic exposure than nonliposomal proteins. The protein VEGF-C156S was radiolabeled with Iodine-125 by a modified chloramine-T method and encapsulated into liposomes. The protein was injected at a dose of 125 μg/kg to mice i.v. or s.c.; the liposomal preparation was administered s.c. (s.c. Lipo). Blood and lymph nodes were collected over 24 h. The mean residence time in lymph nodes after s.c. or s.c. (Lipo) administration was approximately double that following i.v. administration. The area under the concentration-time curve (AUC) ratio of lymph node-blood after s.c. administration of VEGF-C156S was more than double of the AUC ratio after i.v. administration. The results suggest that lymph node exposure of VEGF-C156S was significantly higher after s.c. administration of liposomal or nonliposomal protein as compared with i.v. administration.

Topological transformation of liposomes by a membrane-affecting domain of recombinant human erythropoietin

Recombinant human erythropoietin (rh-Epo) is well accepted as a hematopoietic drug, but many other pleiotropic properties are currently under investigation. Rh-Epo-induced receptor-mediated signal transductions are accompanied with membrane dynamic processes, which facilitate the activation of individual pathways. However, its direct effect on membrane dynamics is still unknown. In the present study, we have proven the capability of rh-Epo to associate to and transform artificial lipid membranes. Association studies using neutral, negatively, and positively charged liposomes with the native as well as modified rh-Epo were performed and analyzed by transmission electron microscopy and differential scanning calorimetry. By these studies, we demonstrated that rh-Epo has the capability to transform negatively charged unilamellar vesicles into so-called disc-like micelles. Rh-Epo association to the negatively charged head groups via lysine and arginine initiates this transformation. At physiological temperatures, conformational changes within the rh-Epo structure expose a defined amino-acid sequence, which is able to induce the formation of discoid membrane structures. Enzymatic digestion, analysis, and isolation of related peptides by rp-HPLC and characterization by MS/MS enabled the identification of the membrane-affecting domain of rh-Epo (MAD-E) that represents the exposed helix B of rh-Epo. Finally, association studies performed with these peptides confirmed that the MAD-E is responsible for the formation of disc-like micelles. Since this helix B of rh-Epo has recently been supposed to be involved in the activation of neuroprotective pathways, we believe that the membrane-transforming capacity of rh-Epo participates in the proliferative activity of rh-Epo.

Erythropoiesis-stimulating protein delivery in providing erythropoiesis and neuroprotection

Erythropoietin (EPO), a glycoprotein, plays an important role in erythropoiesis and neuroprotection. EPO therapies for anemia or neurodegenerative diseases require frequent injections or high-dose systemic administration which may cause unwanted side effects. Various strategies for EPO delivery have been investigated for increasing EPO bioavailability and decreasing side effects, including nano/micro particles, PEGylation of EPO and transport-mediated delivery systems. Nano/micro particles provide EPO with long-term effect and protect EPO against proteolytic cleavage. PEGylated EPO prolong circulating time and reduce injection frequency of anemia treatment. A transport-mediated delivery system enables protein to cross biological barriers. Presently, there is no report about an effective delivery system of EPO for neuroprotection. This review focuses on EPO delivery systems for erythropoiesis or neuroprotection with prolonged duration and enhanced bioavailability.

Interspecies comparisons of pharmacokinetics and pharmacodynamics of recombinant human erythropoietin

Erythropoietin (EPO) has a highly conserved structure among mammals, and thus recombinant human EPO (rHuEPO) has biological activity in various species. This study explores the interspecies relationships of the pharmacokinetics (PK) and pharmacodynamics (PD) of rHuEPO. The PK parameters such as clearance (CL) and volume of distribution (V(ss)) after i.v. doses of rHuEPO were obtained in several species via noncompartmental analysis and were assessed using the traditional allometric approach. Also, PK/PD modeling of rHuEPO concentrations and responses [reticulocytes, red blood cells (RBCs), and hemoglobin] was performed following a range of i.v. and s.c. doses in rats, monkeys, and humans. Nonlinear disposition (V(max), K(m)) and s.c. absorption rate and bioavailability parameters of rHuEPO were examined. A cascade, indirect, lifespan PD model was applied to recover efficacy (S(max)) and potency (SC(50)) of rHuEPO on erythropoiesis and erythroid cell lifespan parameters. Despite nonlinear rHuEPO disposition, CL and V(ss) were highly correlated with body weight (R(2) > 0.92) with allometric scaling exponents of 0.708 for CL and 0.853 for V(ss). The s.c. bioavailability increased with dose in monkeys and humans but appeared to be dose-independent in rats. A correlation between S(max) or SC(50) and body weight was not obvious. However, RBC lifespans obeyed allometric principles. Size dependence was found for PK and lifespan parameters, whereas pharmacologic parameters were independent of body weight.

Dual-action peptides: a new strategy in the treatment of diabetes-associated neuropathy

Peripheral neuropathy is one of the most common and debilitating complications of type 1 and type 2 diabetes mellitus. Recent studies have shown that several small, non-neural peptides possess neurotrophic activity and exert beneficial effects on nervous system function in experimental and clinical diabetes. Two of these, C-peptide and islet neogenesis-associated protein peptide, are derived from pancreatic proteins and use related signal transduction mechanisms. Derivatives of erythropoietin possess similar properties in the nervous system. As a group, these peptides are of increasing interest as leads to potential new approaches in the treatment of diabetes-associated neuropathies and other neurodegenerative conditions. This review addresses the recent advances made with these peptides in the context of diabetic neuropathy, and highlights similarities and differences in their mechanisms of action from the perspective of combination therapy.

Lymphatic Absorption Is the Primary Contributor to the Systemic Availability of Epoetin Alfa following Subcutaneous Administration to Sheep

The contribution of the lymphatics to the absorption and systemic availability of recombinant human epoetin alfa (rHuEPO) following s.c. injection was examined using a cannulated sheep model. Parallel studies were conducted in sheep where a single bolus dose was administered either by i.v. (10, 100, or 1000 IU/kg) or s.c. (400 IU/kg) injection. The first s.c. group served as a control for the calculation of absolute bioavailability. In the second group, the efferent popliteal lymphatic duct was cannulated and peripheral lymph draining the injection site was continuously collected. In the third group, the thoracic duct was cannulated to allow collection of central lymph just prior to entry into the systemic circulation. Blood was periodically sampled from all animals, and concentrations in serum and lymph were determined by enzyme-linked immunosorbent assay. The cumulative amount of rHuEPO recovered in peripheral and central lymph was 83.9 +/- 6.6% and 75.3 +/- 3.9% of the administered dose, respectively, indicating almost complete absorption from the s.c. injection site and minimal clearance during transit through the lymphatic system. After i.v. administration, the systemic clearance of rHuEPO decreased with increasing dose, reflecting capacity-limited elimination kinetics. A pharmacokinetic model was developed to simultaneously fit experimental data for all treatment groups and estimate bioavailability. The direct measurement of >75% of the dose in peripheral and central lymph independently verifies the calculated bioavailability of 87% and demonstrates the major role of the lymphatic route in the overall s.c. bioavailability of rHuEPO after s.c. administration with this animal model.

Drugs for increasing oxygen and their potential use in doping: a review

Blood oxygenation is a fundamental factor in optimising muscular activity. Enhancement of oxygen delivery to tissues is associated with a substantial improvement in athletic performance, particularly in endurance sports. Progress in medical research has led to the identification of new chemicals for the treatment of severe anaemia. Effective and promising molecules have been created and sometimes used for doping purposes. The aim of this review is to present methods, and drugs, known to be (or that might be) used by athletes to increase oxygen transport in an attempt to improve endurance capacity. These methods and drugs include: (i) blood transfusion; (ii) endogenous stimulation of red blood cell production at altitude, or using hypoxic rooms, erythropoietins (EPOs), EPO gene therapy or EPO mimetics; (iii) allosteric effectors of haemoglobin; and (iv) blood substitutes such as modified haemoglobin solutions and perfluorochemicals. Often, new chemicals are used before safety tests have been completed and athletes are taking great health risks. Such new chemicals have also created the need for new instrumental strategies in doping control laboratories, but not all of these chemicals are detectable. Further progress in analytical research is necessary.

Distribution characteristics of entrapped recombinant human erythropoietin in liposomes and its intestinal absorption in rats

Recombinant human erythropoietin (Epo) is frequently administered by intravenous (i.v.) injection for the clinical treatment of renal anemia. Oral (per os; p.o.) administration is desired as an alternative route to i.v. administration, and liposomes have been chosen as a drug carrier. We found previously that after a p.o. administration to rats of Epo entrapped in liposomes before gel filtration, the Epo was absorbed, but variability in the number of days of appearance and in the levels of pharmacological effects, i.e. , the peak of circulating reticulocyte counts (RTC), was observed. The purpose of the present study was to examine the distribution characteristics of Epo in liposomes and intestinal absorption of liposomal Epo in rats by using purified Epo entrapped in liposomes after gel filtration (Epo/liposomes). The distribution characteristics of Epo/liposomes were determined by measuring the Epo in liposomes by a radioimmunoassay, high-performance liquid chromatography and zeta potential measurements. We observed that the protein part of Epo was mostly entrapped in liposomes, and was not adsorbed by the liposomal membrane at middle and high Epo p.o. doses, but the zeta potential of the Epo/liposomes increased negatively with the increase in the Epo p.o. doses. These results suggest that the sialic acid part of Epo entrapped in liposomes may project out from liposomes, depending on the entrapped Epo concentration. Little Epo was adsorbed or penetrated into liposomes when it was added to empty liposomes. After the p. o. administration of Epo/liposomes, the peak of RTC appeared at a 2-day delay on day 6, without variation and without dose dependency in comparison with that after i.v. administration. These results suggest that one of the reasons for the variability may be because the non-entrapped Epo and/or Epo/liposomes itself affected the intestinal absorption of Epo/liposomes. In conclusion, Epo/liposomes without nonentrapped Epo may be clinically useful for the oral administration of Epo.